The present invention relates to glass for an optical transmission body. More particularly, the invention relates to a method of manufacture of glass for optical fiber, consisting principally of a phosphate or phosphates.
Phosphate glass, which is mainly composed of the oxides of three kinds of elements such as phosphorum (P), gallium (Ga) and germanium (Ge) is well known as optical fiber glass. This glass is superior in optical characteristic and shows lower fusing temperature, compared with glass which consists principally of silica, more specifically, silicon dioxide (SiO.sub.2), and is, furthermore, acidic. For this reason, this glass material is just suitable for use as an optical fiber due to spinning by the vessel fusing method utilizing a quartz vessel. Furthermore, the use of this glass material assures an economical supply of optical fibers.
This aforedescribed phosphate glass has been manufactured by a method wherein fine powder of a glass forming oxide, more particularly, soot, is first produced by a gas phase chemical reaction and the fine powder is then gathered in the vessel and vitrified in a heating and fusing process. The gas phase chemical reaction is utilized in the conventional method, as hereinbefore explained, because the soot produced has excellent purity and, in addition, the loss of phosphorum is comparatively low.
A liquid halogen compound of the glass forming element such as phosphorum is used as the starting raw material for the formation of such soot by the aforementioned gas phase chemical reaction. The compounds ordinarily used are phosphorum oxychloride (POCl.sub.3), gallium trichloride (GaCl.sub.3) and germanium tetrachloride (GeCl.sub.4). These compounds are vaporized and supplied to a reaction tube as a mixture with a carrier gas for oxidation under a high temperature. Thereby, the chlorine (Cl) is separated as chlorine gas (Cl.sub.2), and the phosphorum, gallium and germanium combine with the oxygen to enable the soot to be obtained. The soots are gathered in a quartz vessel and fused by a heating process, so that said soots are vitrified. Therefore, the lower part of the vessel is previously formed in the shape of a nozzle and is closed until vitrification is completed. When vitrification is completed, the temperature is lowered a little while the soot is in liquid condition. The glass fiber, more particularly the optical fiber, may then be obtained by releasing the glass material through the nozzle end of the vessel.
Another well known method of manufacturing glass material consisting of respective oxides of phosphorum, gallium and germanium considers the fact that the gallium forms a very stable phosphate of gallium phosphate (GaPO.sub.4) by reacting with phosphoric acid. In this method, the soot of GaPO.sub.4 is obtained by the flame hydrolysis method of placing both POCl.sub.3 and GaCl.sub.3 in an oxyhydrogen flame in a vaporized condition. The soot consisting of the complex oxide of P.sub.2 O.sub.5 and GeO.sub.2 is mixed with the soot of GaPO.sub.4 and these soots are heated and fused. In this method, the phosphorum is in the forms of GaPO.sub.4 and GeP.sub.2 O.sub.7, so that, as a result, the loss of phosphorum by vaporization can be kept very low.
The aforedescribed two method have common disadvantages. Specifically, it is difficult to control the component ratio of soot and the soot formation rate is low. In other words, the controlling of soot formation by gas phase chemical reaction is difficult, because the reaction occurs for a very short time in the flame, showing an unstable thermal characteristic, and, in addition, the reaction rate is low, based on the essential nature of gas phase reaction. As a result; soot of only several tens of grams can be obtained by a reaction lasting as long as an hour. Furthermore, part of the halogen compound used as the raw material is exhausted from the vessel while it is in non-reacted condition. As a result, the yield is low.
The aforedescribed disadvantages prevent mass-production and economical production of optical fiber.
The principal object of the invention is to provide a method of manufacture of glass for optical fiber, which method provides a high yield.
An object of the invention is to provide a method of manufacture of glass for optical fiber, which method prevents loss of phosphorum due to vaporization.
Another object of the invention is to provide a method of manufacture of glass for optical fiber, which method provides glass-forming compounds with extraordinarily high efficiency.
Still another object of the invention is to provide a method of manufacture of glass for optical fiber, in which method the glass-forming oxide is provided by a liquid phase reaction, so that the reaction occurs at a low temperature, the yield is high, and a large amount of glass-forming oxides can be manufactured by the reaction in a short period of time.